As related art in automotive networking, the CAN (controller area network) protocol has been used for several years. In that case, the communication is controlled in an event-driven manner. Very great loads can be produced when the transmission of various messages is to be initiated at the same time. The non-destructive arbitration mechanism of CAN guarantees the sequential transmission of all messages according to the priority of their identifiers or identifications. For hard real-time systems, an analysis of the transit times and bus loads for the entire system must be made in advance, to make sure that all message deadlines can be observed (even under peak load).
There are already communication protocols which are based on time-controlled processing, such as TTP/C or Interbus-S. The exceptional feature in this case is that the bus access is already planned in advance by allocating transmission instants. Thus, no collisions can occur during the transit time. However, in the same way, a peak load is avoided on the communications bus. Thus, the bus is frequently not completely utilized to capacity.
When working with such time-controlled systems—systems having distributed clocks—synchronization mechanisms are necessary and known, such as synchronization to level changes of individual bits, etc.
Because of this, intervals are frequently necessary between individual messages to compensate for tolerances, thus reducing the efficiency of the bus capacity utilization.
It is apparent that the related art is unable to deliver optimal results in every respect.